1. Field of the Invention
The present invention relates to an additive for skim coat mortar and a skim coat mortar composition including the same, and more particularly, to an additive for skim coat mortar capable of improving workability and surface luster by applying cellulose ether obtained by blending two or more kinds of cellulose ether having a different degree of substitution in a specific range, respectively, and a skim coat mortar composition including the same.
2. Discussion of Related Art
Cement mortar is a mixture of cement, aggregate, and other admixtures with water in the form of dough and can be classified into tile cement mortar, cement plaster, skim coat mortar, plain mortar, and the like depending on its use.
The skim coat mortar refers to a white cement-based finishing material used for building structures. That is, the skim coat mortar mainly includes white cement and limestone and is mainly used in areas of high temperature and humidity such as Southeast Asian areas.
Further, the skim coat mortar is usually applied to a thickness of 1 to 3 mm on inner and outer walls and a ceiling of a building. After the application, the skim coat mortar may be cured only or the cured skim coat mortar may be coated with paint as a finishing process.
If the paint is used for the finishing process, an amount of paint used is closely related to a water absorption rate of the cured skim coat mortar. Therefore, the water absorption rate of the cured skim coat mortar is a main evaluation item as a criterion of an amount of paint used.
Furthermore, cellulose ether such as methyl cellulose, hydroxyethylmethyl cellulose, hydroxypropylmethyl cellulose, hydroxyethyl cellulose, or ethylhydroxyethyl cellulose is added to the skim coat mortar, which provides the skim coat mortar with effects of improvement in workability, improvement in a water retention property, reduction of a water absorption rate, and the like.
If cellulose ether is used alone for skim coat mortar, an adhesive force with respect to a working surface is typically improved by improvement in a water retention property. However, there are differences in characteristics among various kinds of cellulose ether. In case of low-viscosity cellulose ether, cracks may occur on a surface due to workability and quick drying of the skim coat mortar. In case of high-viscosity cellulose ether, workability may be deteriorated due to a skinning phenomenon in which a film is formed on a surface of the skim coat mortar.
Therefore, in order to solve problems of the case where cellulose ether is used alone for the skim coat mortar, there have been made attempts to partially improve workability and a pot time by adding additives to cellulose ether. However, in case of adding some of the additives, there are a lot of lumps which are not well mixed, and as time goes on, a working surface becomes rough and a consistency of dough gradually increases, which may cause problems of working and complaints from workers and may reduce efficiency of working.
Thus, the present inventors studied a composition for skim coat in order to improve the above-described problems and completed the present invention by finding out that if two or more kinds of cellulose ether having a degree of substitution in a specific range are blended, workability and surface luster can be improved.